position:sticky should stick for the enclosing overflow ancestor

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index aa8d0e1601e68c17665463eacacb33799dc2366d..6649dd2f5066b5a343dcf1100b002facf4b1f329 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -609,6 +609,18 @@ TransformationMatrix RenderLayer::renderableTransform(PaintBehavior paintBehavio
     return *m_transform;
 }
 
+RenderLayer* RenderLayer::enclosingOverflowClipLayer(bool includeSelf) const
+{
+    const RenderLayer* layer = includeSelf ? this : parent();
+    while (layer) {
+        if (layer->renderer()->hasOverflowClip())
+            return const_cast<RenderLayer*>(layer);
+
+        layer = layer->parent();
+    }
+    return 0;
+}
+
 static bool checkContainingBlockChainForPagination(RenderLayerModelObject* renderer, RenderBox* ancestorColumnsRenderer)
 {
     RenderView* view = renderer->view();